Reactor Hints


well, since there are so many questions about reactor i figured i would try and pass along my hints for reactor. although many people will know HOW to do this, they may have not thought of it.

  1. Want quick and easy cloth? a great way to have a still cloth made (relativly) quickly is to create a reactor setup with your cloth and objects that you want it to interact with. you can then create the animation and choose a key where the cloth looks best to you. use the snapshot too (tools >> snapshot) and voilia! instant cloth. if you didn’t use a lot of iternations for the plane then you can smooth the cloth a bit and it will look better. remember, the more iternations the more accurate.

  2. things suddenly exploding? lower your colision tolerance (utilities >> reactor >> world) and things won’t explode. i reccomend .3

  3. objects passing though each other? raise your substeps (utilities >> reactor >> preview and animation >> substeps/key). this will increase the amount of calculations max has to do and therefore there is less likely for an object to go past the collission detection between substeps and pass through the object.

  4. after you assign a cloth (or rope) vertex to a rigid body, do you get a message saying no vertex assigned and ignoring constraint? this is kinda funky but ive noticed there is a definite series of steps to do to get this to work.
    a. select the vertex
    b. create the constraint (its near the bottem of the cloth modifier) with vertex STILL SELECTED
    c. choose the constraint and then pick the rigid body (VERTEX STILL SELECTED)
    d. preview (VERTEX STILL SELECTED)
    e. hopefully it all worked, and you should be able to deselect now. if you watned to do another vertex to another rigid body (this DOES work, ive done it) then you repeat the process. if… you happen to lose the first one that you made (or the constraint gets switched to the new vertex) delete the old constraint which had the rigid body nothing is attached too anymore, and repeat the steps.

its kinda fiddly so it sometimes takes multiple trys for it to work.

  1. for pretty much any object more complicated than a primative (ie: got holes, grooves which you want rector to see, etc) your probably going to have to make the rigid body a concave mesh (property editor >> concave). to be sure… you can test its convexity! (reactor >> utiliites >> convexity test)

  2. rope object streching a lot? you can make it so that it keeps its shape (hit constraint, its the other option instead of spring) if an object is attached to it the rope may still strech, so increase the mass of the rope from 1 and it should deal with the stretching.

  3. cloth/rope object? going through itself. in their respective modifiers hit “avoid self intersections” and it should help with this. if its still not doing what you want you can increase the various stiffness, fold stiffness, etc of the objects so that they can’t phyiscally reach that point of self-intersectons.

hope this sorta helped, any other people with hints are certainly welcome.


On ya Largo 39, im working with reactor and its great to have an idea how other people are going with it. I know most of these problems and it just reinforced my thoughts on how i do things. thanks again mate

Cheers have fun


now only if you had posted this like 2 years ago when i first started learning reactor!!! --good pointers


haha, if only i had learned max 2 years ago.

thks guys. ill keep posting if i can thing of more. other posts are welcome too!


just another quickie. i have an experiment which i need to finish and then ill post that one.

  1. waves don’t seem high enough in water? mess around with the wave heights. i had to get mine into the 100s before it started looking like what i wanted.

  2. want to have reactor react to something you animated? your going to have to make reactor start at frame 1 (or 1 frame after the animation starts). utilities >> reactor >>> preview and animation >> start frame. essentially, reactor treats objects with having an animation as having a velocity. so whenever reactor starts, it takes the velocity of all the objects in the scene. if the frame is just when the thing starts to move, then it has no velocity yet and doesn’t move in reactor. putting it one frame AFTER it starts gives it a velocity and thus it hopefully goes through with its animation.

edit the ridgid body object that you will animate has to be set to “unyeilding” for that to work.


sorry for annoying you, but where do i find this? if you are talking about the reactor menu on the top of the max window, all i see is preview animation which has no submenu but opens the preview window.


You need to start by accessing the utilities tab. This is among all the other tabs in the upper right, like modifiers, helpers, etc.
From there, it should be pretty easy to find the reactor section.


oh, yeah, sry. do what he just said.

sry for the confusion.


Thanks a lot for the tips!.

I have a problem with a curtain, in my scene i have a plane for curtain that moves reacting to a rigid body asigned, its all ok, but… some kid of “wind” from the back of the scene is moving the curtain in the animation, and i dont know how to stop it.

any idea? :confused:




although i don’t have max open right now to give specifics, some things you might try

making the curtain heavier

subdividing it more (for better accuracy). along the same lines: adding more substeps

you can also fiddle with the various specifics of the cloth modifier. things like fold stiffness and stuff like that will make the curtain fold less as often and not look like wind is effecting it.





another hint.

one thing that i noticed about reactor is that when you start to have more and more elements in the simulation, you start to lose accuracy. for example, i have an animation where a ball falls down a rollar coaster and had to make a jump. after setting it up so where it made it, i then added a few concave meshes for the track afterwards (not effecting the jump track at all) and then suddenly it wouldn’t make the jump anymore! the answer to that particular problem was probably to just increase the substeps, but for stuff that will be deformed through reactor (ie: cloth, water, rope) there is a way to break up the caluclations amongst independant systems.

for example, lets say i had a curtain fluttering near a window and a shirt falling to the floor. normally i would calculate both at the same time, but since they are essentially seperate systems (ie: the movements of one doesn’t effect the other) i can have reactor calculate only ONE of them at a time using the snapshot tool. essentially what this does is create a copy (or instance or w/e) of the the deformations of the cloth si you can then delete the original from the system and get rid of those calculations. you can then do the same for other cloth or water caluclations until you have multiple snapshotted meshes which make up the overall scene.

why not use mesher? well the thing with mesher is that its more ilike an “instance” and not a copy, so if you delete the original cloth which had the reactor stuff with it, the mesher object goes away too. or if you set the original cloth to “inactive” (not calculated in the system but still there) than the mesher object goes inactive and doesn’t move either.

now, like i said, you can’t do thise with rigid bodies because the object is not being deformed, just moved around. there is probably still another way i just need to experiment with it a bit.


this actually does NOT seem to work for water, possibly because its bound to a space warp. you can still do meshers and stuff and make a single snapshot of the plane, but just not an animation. i guess ill keep messing with it.


water 101

  1. create your hollow box to have the water in

  2. create the water (in the middle of the box)

  3. get to the water specifications (modify), and check “landscape” and pick the box (the container for the water, the ripples will bounce off of it).

  4. create a plane with lots of subdivisions (10 by 10 or 20 by 20 is usually good)

  5. also put plane in the middle of the box.

  6. click on the “bind to space warp” button and bind the plane to the water.

  7. create some sphere or object above the water (so that it falls, starts the ripples)

  8. create a rigid body collection

  9. include the sphere and the box (NOT THE PLANE) in the collection

  10. give the sphere some mass, make the box a concave mesh (both are found in “open property editor”).

  11. test!!

edit this tut is FOUND IN YoUR HELP FILES. USE THEM.
edit2 if you notice that the ball falling into the box is just “bouncing” on top of thin air, this means that your box is NOT CONCAVE. setting it as a concave mesh means that its more complicated (ie: stuff with holes in it, depressions that you want calculated, etc) and thus max calculates it with the holes. i believe the official definition is something that like with a normal mesh a line passes through the object once, but if its concave than it passes through twice (ie: it would pass through one part of it, hit the hole, and then pass through the other part, hence twice).


hey, I’m new to reactor cloth and I must say the post on the sites really great! helped a lot. right now I’ve done something really simple, just a plane and a sphere… plane = cloth sphere = rigid body…

after simulation… plane falls nicely over sphere .yay success…

now the problem I face is this…

each time I animate the sphere … the plain/cloth stays put and doens’t follow… I’ve also attatched it to the sphere. . but don’t know why it still doenst work… could you guys help me out? I’d really appreciate it… thanks!


woah! didn’t see your post! sry.

if you want your cloth to react to the sphere more, your going to need to have the animation of the sphere within reactor (basically set the keys for the animation then set the start frame of reactor to 1). now… depending on how fast the spehre is moving, the cloth may stay on top of it, or it may just slide off (since it is a sphere after all), you might try increasing the friction of the sphere (its in the properties thing) and hopefully it will stay on better, but you may get some issues witht he cloth initially falls on the sphere.

once you have the sphere moving where you want, and the reactor frame start set to when the sphere starts to move, ur going to need to redo the reactor key stuff so that it updates all the movements with the sphere.

for a more detailed answer ill need what youve done with the sphere & cloth, and what your trying to do (so that i can try and recreate it and tell you want i did)


i am trying cloth for the first time now…i did some testing…but still dont understand it completly…

i built an ORC from a scetch an i want to have simple cloths going down from his BELT.

(type forest troll in google and see the First picture to see what i mean)

now i asking myself how do i get the cloth beneath the belt (as a layer between skin and belt)

cloth does not allow me to intersect with objects?!

can someone give me the solution for this?

my next problem is:when i chose the belt and the orc mesh as a deformable body,the preview says:my vertex numbers are to high.
or something like that…(the mesh is not that complicated)

so how can i get this cloth attached to the belt and moving with the legs (pushing the cloth)?

i hope you understand my little problem.Please keep your answers detailed and simple cause my englisch is not the bes :slight_smile:

I will get Clothfx soon…my question on FX…does it allow intersections?think not…but how the make this belt things? :-?




mk, well… first thing you will need to do is make SURE your collision tolerance is set to .3 (see earlier in this topic), that way you CAN place the cloth, belt, and leg close to each other. now, for the intersections, the main way to stop it from intersecting is by increasing the amount of substeps per key (again, see previously in the topic) so that it does enough caluclations.

As for deformable meshes, ill have to experiment with that. Most of the cloth stuff that ive done is with rigid bodies and that works perfectly, so unless you could make your leg a rigid body and still have ti wrok right (or set up like a “skeloton” of the rigid bodies of the leg that the cloth can work with and then match those motions to like the bones on the leg or something), ill have to look at that tonight and see what i can come up with.

For the error, it looks like its not complaining about the COMPLEXITY of your mesh, just how many verticies there are. so if you had meshsmoothed your leg than, although it may not be all that complex a shape, it has a hell of a lot of verticies and therefore max complains (its probably a thing where max sets a limitation on that in order to stop it from killing your comp or causing it to crash, i can easily see how a DEFORMABLE mesh would be killer on your memory). So i woul dhave a non-meshsmoothed version of the leg in which you apply the calculations too, and then meshsmooth it afterwards (the cloth may intersect slightly or not quite be perfect… but it will be close enough).


Soft Body setup/hints

basics on setting up a softy body simulation (for example… a pillow, or something which, when colliding with a hard object, will deform. so…pillows…waterballons…bubbles…etc)

1: apply the soft-body modifer to the object.
2: create soft body collection
3: include the object in the collection
4. create rigid body collectiona nd include the 'hard" object in there that won’t bend or w/e
5. animate!

general tips:

  1. this needs a higher substep count (25 is like the minimum)
  2. this will take longer to render (its deforming the mesh)
  3. ive noticed its better to have “avoid self-intersections”, it looks cleaner and more realistic, smae for cloth
  4. obviously, the less stiffness the more it will collapse

meshbased vs ffd based

  1. meshbased:
    a. good: more realistic, deforms the mesh directly
    b. bad: longer to render, sometimes there is reactor funkiness which you have to tweak, no keys (why is that? because it would be like keyframing the individual motion of the VERTICIES of the mesh… ewwwwww)

  2. ffd based:
    a. good: fast, THEREA RE KEYS! you can animate the control points! yay!
    b. bad: what its doing is animating the collapse of the FFD box, and NOT the mesh directly, the mesh is then deformed by the ffd. for example, if you had a sphere hit a floor, with meshbased it would deform in the center with folds and stuff etc. but in ffd the ffd box would fold up like an accordian and the mesh would do likewise. its a different kind of deformation.



hinges are pretty easy to set up, but can be kinda tricky to get working, and have some oddnesses which im not really sure whats going wrong.

but anyways. setting up:

  1. create yoru two hinged pieces, include them into a rigid body collection
  2. create hinge constraint, choose the two pieces (one to be the parent, one the child, child is what hinges on the parent)
  3. set alignspaces to parent body
  4. create constraint solver, include the hinge constraing, and also pick the rigid body collections under the appropriate button
  5. voila! hinge is set up

hints on getting it to work

  1. make sure to give teh child mass! and sometimes when messing with hinges it sets the child to inactive, dunno why but it does
  2. when you move the child around, u will notice the constraint moving as well. this screws things up, so make sure to align it back to parent body after moving
  3. sometimes the thing just will not move, my current theory si that there is a minimum momentum that the child needs before it begins to move, so try making the angle a bit more exteme (so for example, if you had a vertical setup like dominos, try giving the child a bit more angle so that it starts to swing down). why the minimum velocity? probably because the hinge constaint prefers getting “pushed” into action (again with domino example, some ball/finger hitting the child to start it moving).
  4. so you have it moving, its swings down and around and… stops!!! why? well… again witht he minimum momentum, perhaps on the upswing it just doesn’t have enough momentum to retrigger the hing and thus start going down again. ive noticed that increasing the mass of the child makes pretty much no difference (so i guess its more velocity based and not momentum, which includes mass, hehe), and the only really way ive been able to solve this is to have the child father out from the hinge so that it builds more speed downwards and thus has enought o trigger it again. messing around with the strength doesn’t do anything, that determines the strength of the bond between them (0 means… there isn’t and it just sorta flys). tau… doesn’t really do it either, not sure what it DOES do yet.


after using rector for some time, lately i get an error message when i want to activate the animation preview that the setting of the pixelformat fails. i cannot imagine what this means, so i join the maxscript:
thanks for help -